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The process of extracting crude oil and making it ready for consumption is often entangled with many problems. The production and reservoir engineer is often burdened with ensuring that these problems are prevented, managed and controlled. Failure to prevent these problems could lead to loss of resources, lives and facilities.
Problem well analysis which involves the study of a particular oil or gas through the collection well data at given points to ascertain any potential problem and also prevent it must be handled on a reservoir basis, area basis, or individual well basis. Therefore, the well analyst must be certain of the particular problem in order to solve it and maximize production. It is also imperative for him to define the caus of a problem so that the right and appropriate solution can be proferred.
There are different kinds of wells and well problems varies from well to well. In producing well, a problem may be related with specific limits to low oil or gas production, high water cut (WOR), mechanical problems, high gas oil ratio (GOR), depending on the economics of a particular situation. For instance, in an injection well, the well problem may be related to low injection volumes or high injection pressure.
As aforementioned, the symptoms of well problems are recognized through regular collection and analysis of individual well production data and these data are sometimes supplemented with other data. However, a general program or ways for detecting well problems are; regular observation of production characteristics, routine checks of surface pressure on production and surface casing strings, regular checks of shut-in pressure to observe unusual decline in pressure (pressure drops), routine temperature survey which may be useful in detecting large leaks et cetera.
Having detected well problems, a proper analysis will always result in one of the following recommendations or solutions;
workover operations: this refers to one or more varieties of remedial or correctional operations performed on a producing well in order to increase or restore production. Examples of workover operations are well stimulation and routine maintenance work.
continue well production until gas or oil production declines to a certain economic limit or a predetermined volume.
pressure maintenance: some well problems are usually as a result of low or high well pressure. Balancing the formation and hydrostatic pressures could be a common solution then.
Enhanced Oil Recovery: which involves the use of artificial lift systems
shut-in or well abandonment for a time being: in worst cases of well problems
Also to note is that, gas well problems and oil wells problems are usually similar except that gas well problems include liquid loading problems which is more difficult to handle. But generally, well problems can be categorized under the following; limited producing rate, sand production, excessive water production, excessive gas production for oil wells etc source
The problem of low productivity or limited producing rate may be as a result of low reservoir pressure for depth, low permeability, formation damage, mechanical failures, inadequate artificial lift, wellbore or tubing plugging, excessive back pressure on formation and many more.
Talking of low reservoir permeability, it may be an overall reservoir characteristic, or it may be limited to a specific area. If low permeability has been proved as a cause of limited production in a well, this problem should be considered along with other possible causes of low permeability. In low permeability reservoirs, well productivity reduces rapidly as fluids near the wellbore are produced. If available geologic and reservoir data do not readily prove low permeability, production tests and pressure build-up tests may and in differentiating low permeability to formation damage. In this case scenario, a possible treatment or remedy would be hydraulic fracturing.
This is a very serious problem in producing wells that can often lead to lost circulation or fluid loss into the formation. Reservoir pressure measurements should be done or carried out on routine basis and the reservoir pressure history should be recorded for history matching purposes. If in a well, low productivity is due to low reservoir pressure, the next step is to consider the dominant reservoir drives in a particular reservoir and how these drives mechanisms are associated with the real or apparent well problem being instigated. With the aid of pressure guages and drawdown tests, reservoir pressure can be detected and pressure maintenance can be recommended based on the dominant reservoir drive.
Formation damage entails any impairment of well productivity or injectivity due to plugging within the wellbore, perforations, formation pores adjacent to the wellbore, or fractures communicating within the wellbore. It is always pertinent to determine the degree of well damage, causes, and approaches to alleviate any damage caused. The basic cause or formation damage is contact with a foreign fluid such as drilling mud, workover or completion fluids, well-treating fluids etc.
Formation Damage can be diagnosed through several processes such as production tests, comparison with off-set wells, pressure build-up tests, analysis of production history etc. When formation damage is the well problem, its remedy will always be well stimulation.
There are numerous well problems but ill pause our discussion here. Maybe I subsequent articles, well discuss them. I hope you find this piece insightful and informative.
References
https://www.onepetro.org/conference-paper/SPE-5605-MS
https://www.researchgate.net/deref/http%3A%2F%2Fdx.doi.org%2F10.1016%2FB978-0-12-809374-0.00012-X
https://www.researchgate.net/publication/314071531_Well_Problem_Identification
https://www.slb.com/resource-library/oilfield-review/defining-series/defining-formation-damage
https://petrowiki.org/Formation_damage
http://www.oilfieldwiki.com/wiki/Overview_of_Formation_Damage
https://www.glossary.oilfield.slb.com/en/Terms/r/reservoir_pressure.aspx
https://petrowiki.org/Reservoir_pressure_and_temperature
https://wiki.aapg.org/Production_problems
